Biodiesel fuels are methyl esters or ethyl esters of long chain fatty acids derived from renewable, primarily agricultural sources, such as vegetable oils or animal fats for use in diesel engines. Biodiesel is produced in a pure form (100% biodiesel fuel is referred to as “B100” or “neat biodiesel”) and may be blended with petroleum-based diesel fuel. Biodiesel blends are denoted as “BXX,” with “XX” representing the percentage of biodiesel contained in the blend (i.e.: B20 is 20% biodiesel, 80% petroleum diesel, B2 is 2% biodiesel, 98% petroleum diesel and B5 is 5% biodiesel, 95% petroleum diesel. Several standard-setting organizations worldwide have adopted biodiesel specifications. ASTM International has approved a specification for biodiesel referenced as D 6751. As used herein, and as accepted in the art, the D numbers refer to ASTM Standards; ASTM, 100 Barr Harbor Drive, West Conshohocken, Pa. 19428-2959. In addition, German authorities have issued a provisional specification for fatty acid methyl esters under DIN 51606. Europe's Committee for Standardization (“CEN”) is setting a technical standard for biofuels to be referred to as EN 14214. According to the Engine Manufacturer's Association (EMA), depending on the biomass feedstock and the process used to produce the fuel, B100 fuels should meet the requirements of either ASTM D 6751 or an approved European specification, such as DIN 51606 or EN 14214 (once adopted). These standard setting bodies, therefore, are considered by the industry to represent the current best knowledge in the art.
One issue that arises with the use of biodiesel blends is the cold weather performance of the blends. The EMA has issued a statement regarding premium diesel fuel. This Consensus Position is intended to define premium diesel fuel marketed commercially at retail fueling stations and truck stops. The Consensus Position states that it is the belief of the EMA and The Maintenance Council (TMC) that equipment users look to premium diesel fuel at the pump as a significant opportunity for improving fuel-related performance issues or solving problems related to fuel. Among the most significant aspects of this recommendation was a reference to improved cold weather performance. Regarding cold weather performance, the statement includes a discussion of several tests that are said to be commonly used to characterize the low temperature operability of diesel fuel. These are Cloud Point, Low Temperature Flow Test (LTFT), and Cold Filter Plugging Point (CFPP). Among these, the paper indicates that LTFT provides the best overall correlation with field performance, and that, for non-additized fuel, Cloud Point and LTFT correlate very well. Since Cloud Point is more practical as a quality control test, it is listed as the primary recommendation.
Another organization that is recognized in the field as representing the current state of knowledge in the art is the National Biodiesel Board (NBB). The NBB describes itself as “the national trade association representing the biodiesel industry as the coordinating body for research and development in the United States.” In a white paper published online by the NBB entitled Cold Flow Impacts, the cold flow properties of biodiesel are discussed. The paper states that “During the last seven years, the cold flow properties of biodiesel and biodiesel blends have been thoroughly tested with a variety of diesel fuels, both with and without cold flow enhancing additives. Biodiesel blends (primarily B20) have also been used in a variety of climates—including some of the coldest weather on record—without cold flow problems.”
This paper concludes with several statements summarizing the NBB's position on the current thinking in the use of biodiesel in cold weather. These conclusions include the following statements.
(1) Number 2 diesel fuel can experience significant cold flow problems in cold weather.
(2) The diesel industry have met the challenge associated with Number 2 diesel through a variety of means that are in common practice today, i.e., kerosene and cold flow additives.
(3) These same solutions should be used with biodiesel blends to assure satisfactory cold weather performance, focus on the conventional fuel depressing the cold flow values as deep as possible with kerosene and additives while starting with a base fuel that possesses low cloud and cold filter plugging point values.
(4) Incorporation of blends with less than 20% biodiesel (i.e. B5 or B2) into existing diesel fuel has demonstrated little or no negative effect on the cold flow properties of the finished blend, however, it is very important to ensure observation of cold flow properties of base fuels and ensure proper blending principals of diesel and biodiesel.
The State of Minnesota began requiring the use of at least 2% biodiesel in biodiesel blends in the state as of September 2005. In the fall following the mandate there were no reports of filter plugging, but some anecdotal evidence of certain fleets experiencing an increase in filter changes. December of 2005, however, brought the first period of temperature below 0° F. and during this cold weather there were numerous reports of filter plugging with B2 blends in all areas with all brands of diesel fuel. In many cases a creamy, paste-like material was reported.
In response to this plugging problem, the NBB initiated a new investigation that resulted in a “Draft” new cold soak filter time test for biodiesel. The Draft NBB filtration time test is performed essentially as follows:
The original sample container is well mixed;
A subsample is taken immediately after mixing;
The subsample is chilled at 40° F. for 16 hours and allowed to warm to room temperature without heating;
The subsample is then shaken for 1 minute and a 300 ml portion of the subsample is immediately measured into a 500 ml graduated cylinder and transferred to a filter funnel;
The filter is a 1.6 micron glass fiber filter (Whatman GF/A)
Filtration is under a vacuum of 21 to 25 inches Hg;
The filtration time for the full 300 ml is measured, and a time of 360 seconds is considered acceptable for use in biodiesel blends, at least up to B20.
For the B100 filtration time tests presented in the present disclosure, the filter was supported on a stainless steel mesh that contributed negligible resistance to flow, in contrast to the draft NBB method that uses a glass frit support. An aspect of the present disclosure, however, is that this draft test is inadequate for prediction of cold flow problems.
The present disclosure addresses a problem that is unrecognized by the standard setting and trade association bodies that represent the current state of the art of the manufacture and use of biodiesel products, and especially biodiesel products for use in compression ignition engines in cold weather conditions. The disclosure also demonstrates that the accepted tests for cold temperature performance are inadequate to detect the cold weather problems and provides improved fuels that overcome these cold weather issues.